Tension indicating washer



July 4, 1967 J. D. CUMMING 3,329,058

TENSION INDICATING WASHER Filed April 1, 1965 2 Sheets-Sheet 1 INVENTOR. JJAMES o. CUMMING ATTORNEYS y 4, 1967 J. D. CUMMING 2 TENSION INDICATING WASHER Filed April 1. 1965 2 Sheets-Sheet 2 FIG. 7

' INVENTOR. FIG. 5 JAMES D. CUMMING ATTORN EYS United States Patent 7 Claims. (Cl. 85-62) The present invention relates to tension indicating devices and primarily to devices in the nature of washers which can be used to give an indication of the tension which has been applied to a bolt, one end of'which bears against the washer embodying the invention.

The invention has particular, although not exclusive application to rock bolts which are used in mines, tunnels, rock cuts and other excavated locations to bind together various rock strata so as to stabilize the rock formation and to prevent collapse.

For example, the stability of a mine or tunnel roof driven through rock is affected by faults and fractures, rock stratification, bedding and cleavage planes and the like. In roof locations, the arch in the roof of a tunnel may be stabilized by the use of rock bolts by causing these rock bolts to bind the strata together to set up a frictional bond between them. Rock bolts are anchored, at one end, within the rock body and at the other end, bear upon the exposed face of the rock through the medium of a suitable washer or bearing member. By applying a tension to the bolt against this washer, the various rock strata are held in compression. In general, the ability of the rock bolts to perform the desired task is dependent upon the tension applied to the rock bolts and is roughly proportional to that tension. Without tension in the rock bolts, the strata may slip or rock movement may take place and the arch effect within the roof may be destroyed.

According to conventional practice, rock bolts are provided with an expansion shell at one end and this end is inserted within a hole bored in the rock. A washer is applied over the other end to bear against the exposed face of the rock and a nut is threadably engaged over the exposed end of the rock bolt. As the nut is tightened down, the expansion shell grips the interior walls of the hole and further tightening of the nut causes a tension to be applied to the rock bolt between the washer and the expansion shell.

It is very important in applications of this kind that every bolt be tightened to the desired degree so that all the bolts are exerting an appropriate force upon the rock. The normal practice in applying rock bolts of this kind is to tighten up the nut by means of a torque wrench until a specified torque reading has been achieved. Torque readings, however, are subject to very wide errors and it is frequently impossible to ensure, by this means alone, that every bolt is performing the specified task. It is also very important to ensure that the desired tension in the bolts is maintained during service. Any release or reduction in tension will prevent the bolt from performing its specified task and any increase in tension due to rock movement may impose a tension on the bolt greater than that which it is designed to bear. Torque wrenches are unsuitable for checking the tension in rock bolts during their service life since in the environment in which they are used, corrosion will frequently bind the nut upon the bolt so as to provide an abnormally high torque reading if a torque wrench is used to check the tension after installation.

It is an object of the present invention, therefore, to provide a tension indicating device which, by virtue of its construction, will provide a visual indication of the tension which exists in the bolt and which will, accord- 3,329,058 Patented July 4, 1967 ingly, make it possible to dispense with the use of a torque wrench during installation of the bolt and which will also make it possible to check the installation to ensure that the desired tension is being maintained during service.

It is a further object of the present invention to provide a washer having a tension indicating device which gives a visual indication of the tension existing in the bolt in a manner which does not require careful and precise examination, which does not require the use of special tools or equipment to install and which can be read by an unskilled workman without the use of special tools or instruments.

The present invention is disclosed by way of example, in the accompanying drawings in which like reference numerals denote like parts in the various views and in which:

FIGURE 1 is a perspective view of a portion of a mine tunnel showing representative rock bolts in position to support the roof;

FIGURE 2 is an enlarged cross-section showing one of the rock bolts of FIGURE 1 and illustrating the tension indicating device applied to the washer;

FIGURE 3 is an enlarged perspective view showing, in detail, the tension indicating washer in position adjacent the roof of a mine tunnel and with the device indicating that no tension has been applied to the rock bolt;

FIGURE 4 is a view similar to FIGURE 3 indicating that the rock bolt is now at the desired tension;

FIGURE 5 is a view similar to FIGURE 3 showing an alternative embodiment of the invention;

FIGURE 6 is a detailed enlarged view of a portion of FIGURE 4; and

FIGURE 7 is a detailed enlarged view showing a portion of FIGURE 5 as it would appear if the desired tension had been applied to a bolt associated with the washer of FIGURE 5.

The washer illustrated in the drawings is, apart from the tension indicating device applied thereto, substantially the same as is disclosed in my Canadian Patent No. 660,- 827 of Apr. 9, 1963 and entitled Bearing Numbers for Rock Bolts. The washer itself, apart from the tension indicating device possesses all of the advantages of function and utility which are enjoyed by the bearing member disin a drilling 13 formed in the rock and extending upwardly from the surface of the roof 10. An expansion shell 14 is provided at that end of the rock bolt 12 which lies within the drilling 13. The expansion shell 14 may be of any suitable construction and forms no part of the present invention. In general, expansion shells are constructed so that as tension is applied to the bolt, the shell will expand radially to grip the walls of the drilling 13 and to hold the bolt firmly within the drilling.

The bolt 12 is provided, adjacent its outer end, with screw threads 15 over which is threadably engaged a nut 16. The nut 16 is adapted to seat upon the bearing surface 17 of the resilient dished washer 18, preferably through the medium of a hardened steel intermediate washer 19. As the nut 16 is advanced along the thread 15 from the free end of the bolt 12 towards the expansion shell 14, the bolt 12 will be placed in tension and the rock strata 10a, 10b and constituting the roof 10 will be placed in compression. As this occurs the dished resilient washer 18 will elastically flex from its curved or dished configuration as shown in FIGURES 2 and 3 towards the planar configuration shown in FIGURE 4.

In themanner and for reasons explained in my Canadian Patent No. 660,827 the dished washer 18 will assume a substantially planar configuration at the same time as the desired tension has been applied to the bolt 12. In order to achieve this, the material from which the washer 18 is made and the thickness of that material will be chosen so that it will require a force equivalent to the maximum intended tension in the bolt to elastically deform the washer 18 from its dished or curved configuration to the planar configuration.

It is apparent, therefore, that the amount of curvature in the desired washer 18 could be measured and interpreted as a measure of the tension in the bolt 12. It is also apparent, however, that the accurate measurement of the amount of curvature in the dished washer 18 presents some difficulties. First of all, the washer is usually installed overhead in the roof of a mine or tunnel and is not conveniently accessible. Secondly, lighting conditions in tunnels and mine shafts are frequently relatively dim and this makes it difficult for one to accurately determine the degree of curvature. Thirdly, the accurate measurement of the amount of curvature would be virtually impossible without some form of instrumentation which is a considerable disadvantage since it means that this instrument or device must be carried about the mine and must be used in each case on the washer as it bears on the rough and irregular rock surface. The conditions in tunnels and shafts of mines are frequently such that delicate and accurate instruments might be subject to damage which would make them useless for the intended purpose.

According to the present invention, a tension indicating device is associated with the dished washer 18 so as to provide for a visual indication of the tension existing in the bolt in a manner which makes it easy for an unskilled workman to readily obtain this visual indication without the necessity of using instruments or special devices, and which makes it possible for him to read this indication from the floor of the mine, even in the relatively dim lighting conditions which may prevail.

The tension indicating device of the present invention is illustrated in FIGURE 2 and more particularly in FIG- URES 3 to 7.

The tension indicating element of the present invention comprises a stiff elongated member (as seen in FIG- URES 3, 4 and 6) having two ends 21 and 22. End 21 of the tension indicating element is secured to the convex face 23 of the washer 18 by means such as the weld 24. The tension indicating element comprises a first portion adjacent the first end 21 which first portion lies parallel to, adjacent and in contact with the convex surface 23 of the washer 18. The second portion 25 of the tension indicating element 20 is bent away from the convex surface 23 of the washer 18 and merges with the third portion 26 which lies generally parallel to the first portion adjacent the first end 21 and which extends across a major portion of the width of the convex surface 23 of the washer 18. Conveniently, the washer 18 is of square configuration and the tension indicating element lies adjacent and parallel to one edge. If, however, the washer 18 were to be of circular configuration the tension indicating element would lie along a chord.

Since the tension indicating element 20 is unrestrained except for the portion welded to the convex surface 23 of the washer 18, the angular relationship between the tension indicating element 20 and the washer 18 will vary with the curvature existing in the washer 18 which, as has been explained, will vary with the tension applied to the bolt 12. Accordingly, when the bolt 12 is unstressed, the washer 18 will be dished and curved as shown in FIG- URE 3 and the separation between the free end 22 of the tension indicating element and the convex surface 23 of the washer 18 will be at its maximum. As tension is applied to the bolt 12 by tightening the nut 16 on the threaded portion 15, the force exerted upon the bearing surface surrounding the central bolt-receiving aperture will tend to force the washer 18 from its dished configuration shown in FIGURE 3 towards the planar configuration shown in FIGURE 4. As this deformation of the washer 18 takes place, the changing curvature in the convex surface 23 will, as a result, cause the free end 22 of the tension indicating element to more closely approach the convex surface 23 of the washer 18 and the decreasin g separation between the end 22 of the tension indicating element and the convex surface 23 of the washer 18 will serve as an indication of the tension existing in the bolt 12.

In a simplified form, it would be possible to construct and arrange the tension indicating element 20 in such a way that the free end 22 Would just come into contact with the convex surface 23 of the washer 18 at the time that the desired tension existed in the bolt 12. Such a proposal, however, would have the disadvantage that the workman would have to closely watch the tension indicating element 22 as it approached the convex surface 23 so as to stop tightening the nut 16 at the moment that contact was made. Further, any increase in tension beyond this point due to rock movement would not be discernible since one could not tell whether or not further tension had been applied to the bolt after contact had been made.

Accordingly, the relationship between the tension indicating element 20 and the washer 18 is such that the end 22 of the tension indicating element 20 will remain slightly spaced from the convex surface 23 at the time that the desired tension has been achieved and a stud 27 is provided having a surface 28 which is also spaced from the convex surface 23 and which surface acts as a reference point against which to measure the separation between the end 22 of the tension indicating element 20 and the convex surface 23 of the washer 18. Further, the stud 27 is laterally displaced from the tension indicating element 20 so that as the tension indicating element 20 approaches the convex surface 23 of the washer 18 it may, under the influence of excess tension, approach the surface 23 of the washer 18 more closely than the surface 28 thereby indicating that a condition of over-tension exists in the bolt 12.

In FIGURE 4, the condition of desired tension is illustrated and it can here be seen that the nut 16 has been threaded along the bolt 12 a greater distance than was the case in FIGURE 3 and that a tension has therefore been applied to the bolt 12 which has caused the washer 18 to flex from its dished configuration of FIGURE 3 to a substantially planar configuration in FIGURE 4. As a result of this flexing of the washer 18, the end 22 of the tension indicating element 20 has approached the convex surface 23 of the washer 18 until the lower surface 22a of the free end 22 of the tension indicating element 20 now lies in substantially the same plane as the end face 28 of the stud 27 indicating that the optimum tension exists in the bolt.

FIGURE 6 is an enlarged view showing the relationship between the tension indicating element 20 and the stud 27 carried by the washer 18 and, in dotted lines, the over-tension position of the tension indicating element 20 is indicated.

The construction illustrated in FIGURES 3, 4 and 6 possesses a number of advantages which will be readily apparent. First of all, it is clear that an accurate and readily obtainable indication of the tension in the bolt can be obtained merely by glancing at the tension indicating device and observing its relationship to the end face 28 of the stud 27. Tools or instruments are not needed in order to obtain an accurate reading since if the surface 28 is not flush with the surface 22a of the tension indicating element it will be apparent that a condition of either over-tension or under-tension exists in the bolt and this condition can readily be remedied by either tightening or loosening the nut 16 by the necessary amount.

Further, during manufacture of the washer and tension indicating device, representative samples may be tested and calibrated to ensure that the tension indicating element occupies the appropriate position under the design conditions. Corrective steps may then be applied to the stud 27 to ensure that its end face 28 occupies a position relative to the convex surface 23 of the washer 18 so that under the desired tension in the bolt 12 the two relevant surfaces will lie flush with one another.

An alternative embodiment of the invention is illustrated in FIGURES 5 and 7. In FIGURE 5 the washer 18a is shown having a convex surface 23a which carries a tension indicating element 20a secured thereto by means of a weld 24a in a manner identical to that which has been described.

The washer 18a of FIGURE 5 differs from the washer 18 of FIGURES 3 and 4 in that the reference point against which the position of the tension indicating element 20a is read is provided by a dimple or deformation 30 provided in the material of the Washer 18a itself. The deformation 30 provides a reference point or surface 31 against which the position of the free end 22 of the tension indicating element 20a may be compared. In the embodiment shown in FIGURE 5 the free end 22 of the tension indicating element 20a extends beyond the edge of the washer 18a and is provided with a downwardly bent portion 32 having an edge 33 the position of which relative to the surface 31 determines the tension in the bolt. By means of the downwardly bent portion 32 conditions of both over-tension and under-tension may be determined in a manner similar to that which obtains for the embodiment illustrated in FIGRUES 3, 4 and 6.

In FIGURE 7, the relative position between edge 33 and surface 31 indicating the desired tension is illustrated and it will be clear that if an excess of tension exists in the bolt 12, the edge 33 will pass the surface 31 and will more clearly approach the rock face 10.

It will be apparent that the tension indicating device provided by this invention is extremely simple, economical and quite independent of external instrumentation to obtain a tension indication or reading. It is equally apparent that anindication of tension can be obtained, visually, from quite a distance from the device by merely observing the position of the tension indicating element relative to the reference point provided by either the surface 28 of the stud 27 or the surface 31 of the deformation 30. In the relatively dim lighting conditions of a mine it is quite simple to obtain an accurate reading and, indeed, it is possible to obtain an indication of tension in the bolt in total darkness by merely feeling the washer to determine, by the sense of touch, the relative position of the tension indicating element and the reference surface.

While the invention has been described and illustrated in detail 'with reference to these two embodiments, it is intended that minor modifications may be made in the construction and arrangement of parts without departing from the scope of the appended claims.

What I claim as my invention is:

1. A washer, for use with a bolt to indicate the tension applied to the bolt, comprising a one-piece dished plate of resilient material having a concave and a convex surface and having a central bolt-receiving aperture, a hearing surface surrounding the aperture so that as tension is applied to the bolt, a force may be exerted on the washer in a direction tending to cause the washer to flex from its dished configuration towards a planar configurafit tion, a tension indicating element comprising a stiff elongated member having two ends, a first one of which is secured to the convex surface of the washer so that the member lies with a portion thereof in abutment with the washer of that end but with a second portion thereof adjacent the second free end of the member spaced from but generally parallel to the convex surface of the washer, the application of tension to the bolt causing the washer to flex towards a planar configuration and causing the second free end of the tension indicating element to approach the convex surface of the washer, the separation between the surface of the washer and the said second free end of the tension indicating element constituting a measure of the tension in the bolt.

2. A washer as claimed in claim 1 in which the tension indicating element is welded at its first one end to the convex surface of the washer.

3. A washer as claimed in claim 2 in which the dished plate is of square outline and the tension indicating element lies parallel to and adjacent one edge. 4. A washer as claimed in claim 1 wherein the tension indicating element is bent intermediate its ends to comprise a first portion adjacent its first one end which is parallel to, in abutment with and welded to the washer, an intermediate portion bent away from the washer and a terminal portion adjacent the second free end and generally parallel to the washer but spaced therefrom.

5. A washer as claimed in claim 1 wherein the convex surface of the washer is provided with a projection opposed to, generally normal to and extending towards the second free end of the tension indicating element so that the surface of the projection adjacent the tension indicating element may constitute a reference point from which to measure the separation between the tension indicating element and the surface of the washer. 6. A washer as claimed in claim 5 wherein the pro ection comprises a portion of the washer itself deformed to project towards and generally normal to the tension indicating element at the edge of the washer adjacent the second free end of the tension indicating element, said second free end of the tension indicating element extending beyond said edge and having a portion bent towards the said edge so that the end of the bent portion of the tension indicating element may lie above or below the projection when the washer is flexed towards the planar configuration as tension is applied to the bolt. 7. A Washer as claimed in claim 5 wherein the projectron comprises a stud carried by the washer and extending from the convex surface thereof towards and generally normal to the second free end of the tension indicating element, the stud having a surface remote from the convex surface of the Washer constituting a reference point from which to measure the separation between the second free end of the tension indicating element and the surface of the washer.

References Cited UNITED STATES PATENTS 2,725,843 12/ 1955 Koski -62 2,850,937 9/1958 Ralston 85-50 3,060,731 10/1962 Adise 85-62 3,072,093 1/ 1963 Lanius 85-62 3,104,645 9/ 1963 Harrison 85-62 3,169,440 2/ 1965' Taylor 85-62 CARL W. TOMLIN, Primary Examiner.

G. A. MILWICK, R. S. BRITTS,

Assistant Examiners. 

1. A WASHER, FOR USE WITH A BOLT TO INDICATE THE TENSION APPLIED TO THE BOLT, COMPRISING A ONE-PIECE DISHED PLATE OF RESILIENT MATERIAL HAVING A CONCAVE AND A CONVEX SURFACE AND HAVING A CENTRAL BOLT-RECEIVING APERTURE, A BEARING SURFACE SURROUNDING THE APERTURE SO THAT AS TENSION IS APPLIED TO THE BOLT, A FORCE MAY BE EXERTED ON THE WAHSER IN A DIRECTION TENDING TO CAUSE THE WASHER TO FLEX FROM ITS DISHED CONFIGURATION TOWARDS A PLANAR CONFIGURATION, A TENSION INDICATING ELEMENT COMPRISING A STIFF ELONGATED MEMBER HAVING TWO ENDS, A FIRST ONE OF WHICH IS SECURED TO THE CONVEX SURFACE OF THE WASHER SO THAT THE MEMBER LIES WITH A PORTION THEREOF IN ABUTMENT WITH THE WASHER OF THAT END WITH A SECOND PORTION THEREOF ADJACENT THE SECOND FREE END OF THE MEMBER SPACED FROM BUT GENERALLY PARALLEL TO THE CONVEX SURFACE OF THE WASHER, THE APPLICATION OF TENSION TO THE BOLT CAUSING THE WASHER TO FLEX TOWARDS A PLANAR CONFIGURATION AND CAUSING THE SECOND FREE END OF THE TENSION INDICATING ELEMENT TO APPROACH THE CONVEX SURFACE OF THE WASHER AND THE SEPARATION BETWEEN THE SURFACE OF THE WASHER AND THE SAID SECOND FREE END OF THE TENSION INDICATING ELEMENT CONSTITUTING A MEASURE OF THE TENSION IN THE BOLT. 